The State Resource Center employs around 770 people, serving 230 clients with intellectual or developmental disabilities.

The Iowa Department of Human Services said Wednesday it has taken "significant personnel action".

"State facilities do not tolerate mistreatment of clients and we require staff to report concerns immediately," said Richard Shults, administrator of Mental Health and Disability services for Iowa DHS.

The abuse included staff members teasing, or even striking clients of the Glenwood facility, and allowing one client to assault another, either physically, or verbally.

There are 17 homes on the 230-acre Glenwood campus.

Iowa DHS notes families and guardians of clients who were subject to mistreatment have been notified.

In addition to the six firings, and six resignations, disciplinary action has been taken against five other staff members, and one staff member still faces sanctions.

The majority of the abuse happened during evening shifts.

"We hope the shameful and unacceptable behavior of a few staff will not detract from the dedicated work of the vast majority of staff members that provide high quality services to Glenwood's clients," said Glenwood Superintendent Gary Anders. "We remain committed to serving and treating our clients with the dignity and respect they deserve."

Any staff member may be subject to criminal prosecution, but it was immediately unclear if any charges would be filed.

The Glenwood facility has increased supervision of staff, and is undergoing retraining of all supervisors and managers.